1. Field of the Invention
The present invention relates to a pattern inspection technique in which a defect of a circuit pattern formed on a substrate is inspected, particularly to a pattern inspection apparatus in which a defect of a micro pattern formed in a transfer mask for lithography for use in manufacturing a semiconductor device or a liquid crystal display (LCD), or in a semiconductor substrate or liquid crystal substrate is inspected.
2. Description of the Related Art
In recent years, miniaturization of a pattern size of a large scale integrated circuit (LSI) has advanced year by year, and it is expected that products having a minimum line width of 0.1 μm or less will be mass-produced in the near future. With this miniaturization, the dimension of a defect which has to be detected has been remarkably small, and development of a pattern inspection apparatus which inspects pattern defects of a pattern of the LSI and a mask for transfer for use in manufacturing the LSI has become indispensable.
Moreover, with advances in information techniques and multimedia techniques, in LCDs, enlargement of a liquid crystal substrate size and miniaturization of patterns such as thin film transistors formed on a liquid crystal substrate have advanced. Therefore, it has been requested to inspect a broad range for a remarkably small pattern defect. Accordingly, there has been a pressing need to also develop a pattern inspection apparatus which efficiently inspects the pattern defects of a pattern of such a large-area LCD and a photo mask for use in manufacturing the large-area LCD in a short time.
In a conventional pattern inspection apparatus, optics similar to a microscope are used to enlarge the pattern formed on a plate to be inspected of a mask for transfer at a predetermined magnification and to inspect the pattern. That is, the plate to be inspected is laid on a stage, and the pattern formed on the plate is inspected during stage running. The substrate is irradiated with a luminous flux having such a size that the predetermined region of the pattern are covered by an appropriate light source and condensing optics during inspection. The light transmitted through the plate to be inspected is incident upon a photoelectric device via magnification optics, and an optical image of the pattern is formed on the photoelectric device. The optical image of the pattern formed on the photoelectric device is photoelectrically converted, and sent as detected pattern data to a comparison circuit.
On the other hand, designed pattern data of the plate to be inspected is converted into the pixels in a reference pattern data generator, subjected to an appropriate filtering process, and converted to an image equivalent to the optical image. Thereafter, the image is sent as reference pattern data to the comparison circuit. In the comparison circuit, the detected pattern data is compared with the reference pattern data in accordance with an appropriate algorithm. When the data do not agree with each other, it is judged that there is a pattern defect. It is to be noted that when there is a region of repetition of the same pattern in the plate to be inspected, detected pattern data acquired in the photoelectric device for only a given region is stored instead of the designed data, and used as the reference pattern data for comparison. This system is also generally used.
Image data (detected pattern data) of the pattern defect determined as the defect is stored in the data memory of a computer in order to confirm a situation of the defect after the inspection. On the other hand, since the total data amount of the measured image data is enormous, other normal image data is discarded.
However, this type of apparatus has the following problems. That is, since the detected pattern data corresponding to a non-defect after the comparison is discarded, the detected pattern data at an apparatus abnormal status time cannot be analyzed. Therefore, there is a possibility that a cause-effect relation between the abnormal status of the apparatus and the defect inspection becomes obscure. As a result, there is a problem that the apparatus abnormal status influencing an inspection result is missed. Conversely, there is a problem that an unnecessary re-inspection is carried out and throughput is lowered. When the abnormal status is recognized in the apparatus, there is not any means for confirming a pattern comparison situation at this time, and therefore there is also a problem that reliability of the inspection performed in the past cannot be assured.
It is to be noted that when all the detected pattern data is stored in the data memory, the total image data is enormous. Therefore, this is not realistic for the pattern inspection apparatus which is used at a point of mass production and which carries out a large number of inspections throughout the year.
Therefore, there has been a demand for realization of a pattern inspection apparatus which can inspect the defect of the pattern on the plate to be inspected and by which the cause-effect relation between the apparatus abnormal status and the defect inspection can be recognized and which can contribute to enhancement of an apparatus availability and reliability.